1. Field of the Invention
The present invention relates to a pneumatic radial tire for use in large-sized heavy duty vehicles such as trucks, trailers and the like, more particularly to a heavy duty flat wide base radial tire, and more particularly to a pneumatic radial tire for continuously travelling at high speeds on usual paved hard roads while suitable for use in heavy duty cars such as dump trucks, concrete mixer trucks, garbage trucks or motor trucks for refuse collection and the like which are used on weak grounds other than roads for transporting or conveying debris, building materials, earth and sand in site of construction and diggings.
2. Description of the Prior Art
Tires having tire treads adapted to be used both on paved hard roads and weak grounds have been suggested in for example, U.S. Pat. No. 3,645,314 which include circumferentially elongated longitudinal blocks in a center zone and transversely elongated lateral blocks in side zones in the tread, these blocks being arranged so as to improve the cohesion among the blocks. The tires of this type have generally exhibited a superiority on weak grounds. In continuously travelling at high speeds under a heavy loaded condition on hard roads, however, they have often encountered various failures due to heating accumulated in the tire and decrease of life due to rapid wear in the tread rubber and irregular wear.